Electronic device having a glass component with crack hindering internal stress regions

ABSTRACT

A component for an electronic device including an internal compressive stress region is disclosed herein. The internal compressive stress region may be created in a glass portion of the component or in a glass ceramic portion of the component. Electronic devices comprising the components and method for making the components are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/701,519 filed on Jul. 20, 2018 and titled “ElectronicDevice Having a Glass Component with Crack Hindering Internal StressRegions,” and this application is a continuation-in-part application ofU.S. patent application Ser. No. 16/143,309, filed Sep. 26, 2018 andtitled “Thermoformed Cover Glass for an Electronic Device,” which claimsthe benefit of U.S. Provisional Patent Application No. 62/648,615 filedon Mar. 27, 2018 and titled “Thermoformed Cover Glass for an ElectronicDevice,” and which is a continuation-in-part patent application of U.S.patent application Ser. No. 15/676,860, filed Aug. 14, 2017 and titled“Thermoformed Cover Glass for an Electronic Device,” which claims thebenefit of U.S. Provisional Patent Application No. 62/398,611, filed onSep. 23, 2016 and titled “Thermoformed Cover Glass for an ElectronicDevice,” U.S. Provisional Patent Application No. 62/398,616, filed onSep. 23, 2016 and titled “Thermoformed Cover Glass for an ElectronicDevice,” and U.S. Provisional Patent Application No. 62/398,627, filedon Sep. 23, 2016 and titled “Thermoformed Cover Glass for an ElectronicDevice,” the disclosures of which are hereby incorporated by referenceherein in their entireties.

FIELD

The described embodiments relate generally to glass components for anelectronic device. More specifically, the described embodiments relateto glass components that include internal compressive stress regionsthat may hinder crack propagation through the glass component.

BACKGROUND

Electronic devices often include transparent exterior components. Forexample, transparent cover members both protect and allow viewing of adisplay within the device. However, some traditional glass cover membersmay be susceptible to cracking when subjected to severe impact, such aswhen the electronic device is dropped.

Embodiments described herein are directed to electronic devicecomponents that may have advantages as compared to some traditionalglass components. The techniques described herein are generally directedto components that may include a residual internal compressive stressregion in a glass or glass ceramic portion. The components describedherein may have improved resistance to cracking and therefore provideenhanced durability of the components and electronic devices includingthe components. In general, the components formed using the describedtechniques may not suffer from the drawbacks associated with sometraditional glass components for electronic devices.

SUMMARY

Embodiments described herein relate to components for electronic deviceswhich include a crack hindering residual internal compressive stressregion. The internal compressive stress region may be located in a glassor glass ceramic portion of the component. As examples, the componentmay be a glass component, such as a monolithic glass component formed ofa single piece of glass or a glass laminate. As an additional example,the component may comprise an internal glass ceramic portion andexternal glass portions. The components may be transparent, translucent,or opaque.

In embodiments, the component comprises a residual internal compressivestress region. The residual internal compressive stress region ispresent in the absence of an external load or force. The presence of aresidual internal compressive stress region in the component maystrengthen the component against cracking. Therefore, a glass componentincluding a residual internal compressive stress region may be referredto as a strengthened glass component. The term strengthened glasscomponent may also be used to refer to a component comprising both glassand glass ceramic portions. For brevity, a residual compressive stressregion may be referred to herein as a compressive stress region and aresidual tensile stress region may be referred to herein as a tensilestress region.

The internal compressive stress region of the component may act tohinder movement of a crack through a thickness of the component, therebylimiting damage to the component. For example, the internal compressivestress in this region may prevent a crack from passing through theregion. In some cases the crack may continue to move through thecomponent, but may move in a different direction. For example, the crackmay at least partially reverse direction by moving away from theinternal compressive stress region. Therefore, the residual internalcompressive stress region may deflect a crack propagating through aninternal tensile stress region in the component. The internalcompressive stress region may be in the form of a layer.

In embodiments, the component further comprises at least one externalcompressive stress region. The external compressive stress region mayprovide an initial barrier to generation and/or movement of cracks froma surface of the component into an internal portion of the component.The external compressive stress region may be positioned along at leastone external surface of the component. In embodiments, an externalcompressive stress region may be positioned along front, back, and sidesurfaces of the component. The component further comprises an internaltensile stress region located between the internal compressive stressregion and the external compressive stress region. The internal tensilestress region may be inward from the external compressive stress regionalong a thickness of the component and the internal compressive stressregion may be inward from the internal tensile stress region along athickness of the component. The external compressive stress regionand/or the internal tensile stress region may be in the form of a layer.

As an example, a strengthened glass component for an electronic devicemay comprise a surface at least partially defining an exterior of theelectronic device and a compressive stress region extending from thesurface to a first depth in the component. The surface further definesan exterior of the component. The compressive stress region maytherefore be referred to as an external compressive stress region. Thecomponent may further comprise an internal tensile stress region inwardfrom the external compressive stress region and an internal compressivestress region inward from the internal tensile stress region. Theinternal tensile stress region may extend from the first depth to asecond depth in the component and the internal compressive stress regionmay extend from the second depth to a third depth in the component. Infurther embodiments, the internal tensile stress region is a firstinternal tensile stress region and the component further comprises asecond internal tensile stress region inward from the internalcompressive stress region and extending from the third depth to a fourthdepth in the component.

In additional embodiments, the component comprises multiple internalcompressive stress regions and/or external compressive stress regions.For example, a strengthened glass component for an electronic device maycomprise: a first external surface defining at least a portion of anexterior of the electronic device, a first external compressive stressregion along the first external surface, a first internal tensile stressregion inward from the first external compressive stress region, and aninternal compressive stress region inward from the first internaltensile stress region. The strengthened glass component may furthercomprise: a second external surface opposite to the first externalsurface, a second external compressive stress region along the secondexternal surface, and a second internal tensile stress region inwardfrom the second external compressive stress region. In furtherembodiments, the component comprises a third internal tensile stressregion between the first internal compressive stress region and thesecond internal compressive stress region.

In embodiments, a method for making a component comprising an internalcompressive stress region comprises creating an internal compressivestress region, an external compressive stress region, and an internaltensile stress region in the component. The external compressive stressregion may be along at least one surface of the component. The internaltensile stress region may be inward from the external compressive stressregion. The internal tensile stress region may also be positionedbetween the external and the internal compressive stress regions. Theinternal compressive stress region is inward from the externalcompressive stress region and the internal tensile stress region. Infurther embodiments, the method comprises creating another internaltensile stress region inward from the internal compressive stress regionof the glass component

For example, a method of strengthening a glass component comprisesforming an external compressive stress region extending from a surfaceto a first depth in the glass component. The method further comprisesforming an internal tensile stress region extending from the first depthto a second depth in the glass component and forming an internalcompressive stress region extending from the second depth to a thirddepth in the glass component.

Several techniques can create an internal compressive stress region inthe component. For example, an exchange of ions in a glass or a glassceramic component can create an internal compressive stress region. Asanother example, crystallizing a portion of a glass component to form aglass ceramic can create an internal compressive stress region. Inadditional examples, glass layers having different compositions and/orproperties can be used to create an internal compressive stress regionin a glass laminate component. In embodiments, the glass laminatecomponent comprises a first outer layer formed from a first glassmaterial, an inner layer formed from a second glass material, and asecond outer layer formed from a third glass material. For example, theglass laminate component may comprise outer layers each having a highercoefficient of thermal expansion than that of the inner layer. Asanother example, the inner layer of the glass laminate may have agreater tendency to expand in response to ion exchange than the outerlayers.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be readily understood by the following detaileddescription in conjunction with the accompanying drawings, wherein likereference numerals designate like elements.

FIG. 1A depicts a front view of a simplified example of an electronicdevice.

FIG. 1B depicts a back view of the electronic device of FIG. 1A.

FIG. 2 depicts a simplified example of a cover member for the electronicdevice of FIG. 1A.

FIG. 3A shows a simplified cross-section view of an example cover memberhaving an internal and an external region of compressive stress.

FIG. 3B shows an example of the variation of residual stress across thethickness for the cover member of FIG. 3A.

FIG. 3C shows an enlarged view of another example cover member havinginternal and external regions of compressive stress.

FIG. 3D shows an example of the variation of residual stress withposition for the cover member of FIG. 3C.

FIG. 4A shows a simplified cross-section view of an additional examplecover member having internal and external regions of compressive stress.

FIG. 4B shows an example of the variation of residual stress across thethickness for the cover member of FIG. 4A.

FIG. 4C shows a simplified cross-section view of a further example covermember having internal and external regions of compressive stress.

FIG. 4D shows an example of the variation of residual stress across thethickness for the cover member of FIG. 4C.

FIG. 5A shows a detailed view of an example glass cover member having aninternal compressive stress region created at least in part by an ionexchange process.

FIG. 5B shows an example of the variation of residual stress across thethickness for the glass cover member of FIG. 5A.

FIG. 6 shows a flowchart of a process for making the glass cover memberof FIGS. 5A and 5B according to one embodiment.

FIGS. 7A, 7B, and 7C illustrate stages in the process of FIG. 6.

FIG. 8A shows a detailed view of another example glass cover memberhaving an internal compressive stress region created at least in part byan ion exchange process.

FIG. 8B shows an example of variation of residual stress across thethickness for the glass cover member of FIG. 8A

FIGS. 9A, 9B, and 9C illustrate stages in a process for making the glasscover member of FIGS. 8A and 8B.

FIG. 10A shows a detailed view of an example cover member having aninternal compressive stress region created at least in part bycrystallizing a portion of a glass cover member to form a glass ceramicportion.

FIG. 10B shows an example of the variation of residual stress across thethickness in the sample for the cover member of FIG. 10A.

FIG. 11 shows a flowchart of a process for making the cover member ofFIGS. 10A and 10B according to one embodiment.

FIGS. 12A and 12B illustrate a beam of radiation crystallizing aninternal portion of a glass cover member to form a glass ceramic.

FIG. 12C illustrates a cover member including an internal glass ceramicportion after an ion exchange operation.

FIG. 13A shows a detailed view of another example cover member having aninternal compressive stress region created at least in part bycrystallizing a portion of a glass cover member to form a glass ceramicportion.

FIG. 13B shows an example of the variation of residual stress across thethickness of the glass cover member of FIG. 13A

FIG. 14A illustrates an example glass laminate cover member having aninternal compressive stress region.

FIG. 14B shows an example of the variation of residual stress across thethickness of the glass laminate cover member of FIG. 14A.

FIGS. 15A and 15B illustrate stages of an example method for forming aninternal compressive stress region in a glass laminate cover member.

FIGS. 16A, 16B, and 16C illustrate stages of another example method forforming an internal compressive stress region in a glass laminate covermember.

FIG. 17 shows a block diagram of components of an electronic device.

The use of cross-hatching or shading in the accompanying figures isgenerally provided to clarify the boundaries between adjacent elementsand also to facilitate legibility of the figures. Accordingly, neitherthe presence nor the absence of cross-hatching or shading conveys orindicates any preference or requirement for particular materials,material properties, element proportions, element dimensions,commonalities of similarly illustrated elements, or any othercharacteristic, attribute, or property for any element illustrated inthe accompanying figures.

Additionally, it should be understood that the proportions anddimensions (either relative or absolute) of the various features andelements (and collections and groupings thereof) and the boundaries,separations, and positional relationships presented therebetween, areprovided in the accompanying figures merely to facilitate anunderstanding of the various embodiments described herein and,accordingly, may not necessarily be presented or illustrated to scale,and are not intended to indicate any preference or requirement for anillustrated embodiment to the exclusion of embodiments described withreference thereto.

DETAILED DESCRIPTION

Reference will now be made in detail to representative embodimentsillustrated in the accompanying drawings. It should be understood thatthe following descriptions are not intended to limit the embodiments toone preferred implementation. To the contrary, the described embodimentsare intended to cover alternatives, modifications, and equivalents ascan be included within the spirit and scope of the disclosure and asdefined by the appended claims.

The current description is generally directed to components forelectronic devices, which incorporate one or more internal compressivestress regions. The internal compressive stress region may be located inan internal glass portion or in an internal glass ceramic portion of thecomponent. The component may further comprise an external compressivestress region and an internal tensile stress region between the externalcompressive stress region and the internal compressive stress region.

The presence of one or more internal compressive stress regions mayreduce or hinder the propagation of cracks or defects within the glasscomponent. In some implementations, the internal compressive stressregions may improve the durability and/or impact resistance of the glasscomponent. The techniques and examples described herein may be used tocreate glass components for a cover glass of an electronic device,enclosure components of an electronic device, and other glass articlesthat may form at least a portion of an external surface of theelectronic device. In some instances, the glass component may beinternal to the electronic device or an electronic device enclosure.

As described in more detail herein, the internal compressive stressregions may be formed any number of different ways. In some exampleembodiments, the internal compressive stress region may be created, atleast in part, due to an ion exchange process. The internal compressivestress region may also be created by crystallization of a portion of aglass component to form a glass ceramic. As an additional example, theinternal compressive stress region may be created in an inner layer of aglass laminate having different thermal expansion and/or ion expansionproperties than outer layers of the glass laminate. Electronic devicesincluding the components and methods for making the components are alsodisclosed herein.

These and other embodiments are discussed below with reference to FIGS.1A-17. However, those skilled in the art will readily appreciate thatthe detailed description given herein with respect to these figures isfor explanatory purposes only and should not be construed as limiting.

FIG. 1A depicts a front view of a simplified example of an electronicdevice. As shown in FIG. 1A, the electronic device 100 includes ahousing 110 and a cover member 120. The housing 110 may be formed fromone or more metal or metallic components, a glass component, a ceramiccomponent, or a combination thereof. The housing 110 may include a sidesurface 116. As an example, the side surface 116 may be defined by oneor more metal components. In one example, the side surface 116 is formedfrom a series of metal segments that are separated by polymer ordielectric segments that provide electrical isolation between adjacentmetal segments. As additional examples, the side surface 116 may bedefined by one or more glass components, a glass ceramic component, or acomponent including a glass and a glass ceramic.

The cover member 120 may be formed from a glass, a ceramic, or acombination thereof. As shown, cover member 120 defines a front surface122, which may form at least a portion of an exterior of the electronicdevice 100. For example, the front surface 122 of the cover member 120may define at least a portion of the front surface of the electronicdevice 100. The cover member 120 may be coupled to the housing 110 usinga fastener or fastening technique. For example, the cover member 120 maybe coupled to the housing 110 using an adhesive, an engagement feature,a fastener, or a combination of any of these. As discussed herein, thecover member 120 may include an internal compressive stress region.However, the description provided is not limited to cover members andthe principles described herein are applicable to other electronicdevice components, such as components of the housing 110.

The cover member 120 may be positioned over a display that is configuredto produce a graphical output that is viewable through a transparentwindow region of the cover member. For purposes of the followingdisclosure, the cover member 120 is described as a sheet of glass.However, the cover member 120 may be formed from multiple layers thatinclude glass sheets, polymer sheets, and/or various coatings andlayers. In some instances, a touch-sensitive layer (e.g., a capacitivetouch sensor) is attached to the cover member 120 and positioned betweenthe cover member 120 and the display.

FIG. 1B depicts a back view of the electronic device 100 of FIG. 1A. Thehousing 110 further comprises back surface 114 and side surface 116. Inembodiments, the electronic device 100 may further include a secondcover member, which forms at least a portion of the back surface 114 ofthe electronic device 100. The second cover member may be formed from aglass material that may include an internal compressive stress region,as described herein. The second or rear cover member may be partiallytransparent, formed from a transparent glass sheet, or may be opaque. Insome cases, the second or rear cover includes one or more openings for acamera, light source, or other optical component.

In some embodiments, the electronic device 100 may be a mobiletelephone, a notebook computing device (e.g., a notebook), a tabletcomputing device (e.g., a tablet), a portable media player, a wearabledevice, or another type of portable device. The electronic device 100may also be a desktop computer system, computer component, input device,or virtually any other type of electronic product or device component.

As shown in FIG. 2, cover member 220 may define a front surface 222, aback surface 224, and a side surface 226 extending between the frontsurface 222 and the back surface 224. As shown, cover member 220 isgenerally rectangular and defines a length, L, a width, W, and athickness, T. The thickness T of cover member 220 may be from 0.3 mm to3 mm, 0.1 mm to 2 mm, or from 25 μm to 1 mm. While cover member 220 isdepicted as being generally rectangular in shape for purposes ofillustration, the cover member shape shown is not intended to belimiting. In addition, while the edges 228 between the front surface 222and the side surface 226 and between the back surface 224 and the sidesurface 226 are shown as rounded, the shape shown is not intended to belimiting.

As an example, the cover member 220 may be at least partiallytransparent. For example, the cover member 220 may have a transmittancein the visible spectrum of at least 50% or at least 75%. The covermember 220 may define one or more transparent portions to allow viewingof a display within the electronic device and/or function as a windowfor a camera or an optical sensor. In other examples, the cover member120 may be translucent or opaque over a portion or all of the area ofthe component. The cover member 120 may also include one or more regionsthat are covered with a decoration or an opaque coating.

In embodiments, the cover member 220 includes an aluminosilicate glassor glass ceramic or a boroaluminosilicate glass or glass ceramic. Asused herein, an aluminosilicate glass or glass ceramic includes theelements aluminum, silicon, and oxygen, but may further include otherelements. Similarly, a boroaluminosilicate glass or glass ceramicincludes the elements boron, aluminum, silicon, and oxygen, but mayfurther include other elements. For example, an aluminosilicate glass orglass ceramic or a boroaluminosilicate glass or glass ceramic mayfurther include monovalent or divalent ions which compensate charges dueto replacement of silicon ions by aluminum ions. Suitable monovalentions include, but are not limited to, alkali metal ions such as Li⁺,Na⁺, or K⁺. Suitable divalent ions include alkaline earth ions such asCa²⁺ or Mg²⁺. In embodiments, the aluminosilicate glass may comprisegreater than 0.1 mol % Li₂O or greater than 1 mol % Li₂O. In additionalembodiments, the base composition may comprise from 0.1% to 10% lithiumby weight of the base glass.

FIG. 3A shows a simplified cross-section view of an example cover member320 having an internal and an external compressive stress region. Thecross-section is taken along line A-A in FIG. 2 and hatching is used toindicate regions of compressive stress. The cover member 320 includes aninternal compressive stress region 342, an external compressive stressregion 344, and an internal tensile stress region 354.

As shown in FIG. 3A, external compressive stress region 344 extendsalong the front surface 322, the back surface 324, and the side surface326 of the cover member 320. External compressive stress region 344 mayalso extend around the edge between the front surface 322 and the sidesurface 326. The external compressive stress region 344 may extend fromfront surface 322 or back surface 324 to a first depth D₁. The externalcompressive stress region 344 may take the form of a layer and bereferred to as an external compressive stress layer.

The cover member 320 further includes an internal tensile stress region354 inward from the external compressive stress region 344. As shown,the internal tensile stress region 354 is located between externalcompressive stress region 344 and internal compressive stress region342. The internal tensile stress region 354 may extend from the firstdepth D₁ to a second depth D₂. The internal tensile stress region 354may take the form of a layer and be referred to as an internal tensilestress layer.

The cover member 320 further includes internal compressive stress region342 inward from the internal tensile stress region 354. As shown, theinternal compressive stress region 342 may extend from the second depthD₂ to a third depth D₃. As shown, an internal compressive stress region342 may be centrally located in the cover member 320. As an example, acentrally located stress region may include locations about halfwaybetween front surface 322 and back surface 324 and about halfway betweenopposing side surfaces 326. As used herein, a stress region is inward ofanother stress region when at least a portion of the stress region iscloser to the central portion of the cover member than the other stressregion. The external compressive stress region 344 may take the form ofa layer and be referred to as an external compressive stress layer.

FIG. 3B shows an example of the variation of residual stress withthickness for the cover member of FIG. 3A. The cover member 320 includesan internal compressive stress region 342, an internal tensile stressregion 354, and an external compressive stress region 344. The internaltensile stress region 354 is inward from the external compressive stressregion 344 and the internal compressive stress region 342 is inward fromthe internal tensile stress region 354. As shown in FIG. 3B, a level ofthe compressive stress is greater in external compressive stress region344 than in internal compressive stress region 342.

In additional embodiments, the external compressive stress region maycomprise a first external compressive stress region and a secondexternal compressive stress region. For example, a first externalcompressive stress region may be formed along a first external surfaceof the cover member and a second external compressive stress region maybe formed along a second external surface of the cover member. Thesecond external surface may be generally opposite to the first externalsurface.

FIG. 3C shows a partial cross-section of a cover member 320 including afirst external compressive stress region and a second externalcompressive stress region. The first external compressive stress region344 a may be formed along front surface 322 and the second externalcompressive stress region 344 b may be formed along back surface 324.The cover member may further comprise a first internal tensile stressregion 354 a inward from the first internal compressive stress region344 a and a second internal tensile stress region 354 b inward from thesecond external compressive stress region 344 b. In addition, the covermember 320 may comprise an internal compressive stress region 342 inwardfrom the first internal tensile stress region 354 a. The internalcompressive stress region 342 may also be inward from the secondinternal tensile stress region 354 b.

FIG. 3D shows an example of the variation of residual stress withthickness for the cover member 320 of FIG. 3C. The cover member 320includes an internal compressive stress region 342 inward from first andsecond internal tensile stress regions 354 a and 354 b. First and secondinternal tensile stress regions 354 a and 354 b are inward from firstand second external compressive stress regions 344 a and 344 b. Thefirst and the second external compressive stress regions 344 a, 344 bmay be substantially similar or may differ. The first and the secondinternal tensile stress regions 354 a, 354 b may also be substantiallysimilar or may differ. As shown in FIG. 3D, a level of the compressivestress is greater in external compressive stress regions 344 a, 344 bthan in internal compressive stress region 342. In embodiments, amaximum level of the compressive stress in the external compressivestress regions 344 a, 344 b may be from 3 to 10 times or from 5 to 10times a maximum level of the compressive stress in the internalcompressive stress regions. In embodiments, the surface compressivestress of each of external compressive stress regions 344 a and 344 bmay be from 400 MPa to 800 MPa or from 600 MPa to 800 MPa. As shown inFIG. 3D, thickness of the internal compressive stress region 342 may begreater than a depth of the external compressive stress region 344. Inembodiments, the depth of each of the first and the second compressivestress regions 344 a and 344 b may be from 5 microns to 50 microns.

FIG. 4A shows a simplified cross-section view of another example covermember 420 having an internal and an external compressive stress region.The cover member 420 includes an internal compressive stress region 442,external compressive stress region 444, and internal tensile stressregions 452 and 454.

As shown in FIG. 4A, external compressive stress region 444 extends fromfront surface 422 and back surface 424 to a first depth D₁. As shown,the depth of the external compressive stress region 444 may besubstantially equal around the cover member 420. In further embodiments,the external compressive stress region 444 may vary around the covermember 420. For example, a first external compressive stress region maybe formed along a first external surface of the cover member and asecond external compressive stress region may be formed along a secondexternal surface of the cover member. The second external surface may begenerally opposite to the first external surface. For example, the firstexternal surface may correspond to front surface 422 and the secondexternal surface may correspond to back surface 424. The externalcompressive stress region 444 may take the form of a layer and bereferred to as an external compressive stress layer.

The cover member 420 further includes internal tensile stress region454. As shown, internal tensile stress region 454 is located inward fromexternal compressive stress region 444. Internal tensile stress region454 is also located between external compressive stress region 444 andinternal compressive stress region 442. The internal tensile stressregion 454 may extend from the first depth D₁ to a second depth D₂. Theinternal tensile stress region 454 may take the form of a layer and bereferred to as an internal tensile stress layer.

The cover member 420 further includes internal compressive stress region442. As shown, the internal compressive stress region 442 is inward frominternal tensile stress region 454. As shown, the internal compressivestress region 442 extends from the second depth D₂ to a third depthD_(3.) The internal compressive stress region 442 may take the form of alayer and be referred to as an internal compressive stress layer.

The cover member 420 further includes internal tensile stress region452. As shown, internal tensile stress region 452 is located inward frominternal compressive stress region 442. The internal tensile stressregion 452 may take the form of a layer and be referred to as aninternal tensile stress layer.

FIG. 4B shows an example of the variation of residual stress withthickness for the cover member 420 of FIG. 4A. The cover member 420includes an internal tensile stress region 452, an internal compressivestress region 442, an internal tensile stress region 454, and anexternal compressive stress region 444. As shown in FIG. 4B, a level ofthe compressive stress is greater in external compressive stress region444 than in internal compressive stress region 442.

FIG. 4C shows a partial cross-section of another cover member 420including an internal compressive stress region and first and secondexternal compressive stress regions. The first external compressivestress region 444 a is formed along front surface 422 and the secondexternal compressive stress region 444 b is formed along back surface424. The cover member 420 further comprises a first internal tensilestress region 454 a inward from the first internal compressive stressregion 444 a and a second internal tensile stress region 454 b inwardfrom the second external compressive stress region 444 b. In addition,the cover member 420 comprises a first internal compressive stressregion 442 a inward from the first internal tensile stress region 454 aand a second internal compressive stress region 442 b inward from thesecond internal tensile stress region 454 b. Third internal tensilestress region 452 may also be inward from both first internalcompressive stress region 442 a and second internal compressive stressregion 442 b.

FIG. 4D shows an example of the variation of residual stress withthickness for the cover member 420 of FIG. 4C. The cover member 420includes an internal tensile stress region 452 inward from internalcompressive stress regions 442 a and 442 b. Internal compressive stressregions 442 a and 442 b are inward from internal tensile stress regions454 a and 454 b and internal tensile stress regions 454 a and 454 b areaare inward from external compressive stress regions 444 a and 444 b. Asshown in FIG. 4D, a level of the compressive stress is greater inexternal compressive stress regions 444 a, 444 b than in internalcompressive stress regions 442 a, 442 b. In embodiments, a maximum levelof the compressive stress in the external compressive stress regions 444a, 444 b may be from 3 to 10 times or from 5 to 10 times a maximum levelof the compressive stress in the internal compressive stress regions 442a, 442 b. In embodiments, the surface compressive stress of eachexternal compressive stress regions 444 a, 444 b may be from 400 MPa to800 MPa or from 600 MPa to 800 MPa. A thickness of the internalcompressive stress region 442 a, 442 b may be greater than a depth ofthe external compressive stress regions 444 a, 444 b. In embodiments,the depth of each of the external compressive stress regions 444 a, 444b may be from 5 microns to 50 microns.

In embodiments, an ion exchange process may create an internalcompressive stress region in a component. For example, alkali metal ionsin a glass portion of the component may be exchanged for larger alkalimetal ions at a temperature below the strain point of the glass. The ionexchange process may also create an external compressive stress regionalong an external surface of the component and an internal tensilestress region inward from the external compressive stress region. Theinternal compressive stress region is inward from the internal tensilestress region. In further embodiments, the component further comprisesanother internal tensile stress region inward from the internalcompressive stress region.

For example, the component may comprise an external compressive stressregion including third alkali metal ions having a third size, aninternal tensile stress region including first alkali metal ions havinga first size, and an internal compressive stress region including secondalkali metal ions having a second size. The second alkali metal ions andthe third alkali metal ions may be introduced into the component by ionexchange. The second size may be greater than the first size and thethird size may be greater than the second size. Further, the externalcompressive stress region may be enriched in the third alkali metal ionscompared to the internal tensile stress region and the internalcompressive stress region may be enriched in the second alkali metalions as compared to the internal tensile stress region. In embodiments,the internal compressive stress region, although enriched in the secondalkali metal ions, further comprises the first metal alkali metal ions.

As an additional example, a strengthened glass component may comprise afirst and a second external compressive stress region, the firstexternal compressive stress region along a first external surface andthe second external compressive stress region along a second externalsurface. The first and the second external compressive stress regionseach include third alkali metal ions having a third size. Thestrengthened glass component further comprises a first and a secondinternal tensile stress region, the first internal tensile stress regioninward from the first external compressive stress region and the secondinternal tensile stress region inward from the second externalcompressive stress region. The first and the second internal tensilestress region each include first alkali metal ions having a first size.The strengthened glass component further comprises an internalcompressive stress region inward from the first and the second internaltensile stress regions. The internal compressive stress region includessecond alkali metal ions having a second size.

As a further example, the internal compressive stress region may be afirst internal compressive stress region and the component may furthercomprise a second internal compressive stress region and a thirdinternal tensile stress region. The third internal tensile stress regioncomprises the first alkali metal ions and the first and the secondinternal compressive stress regions are enriched in the second alkalimetal ions as compared to the first, second, and third internal tensilestress regions. In embodiments, the first and second internalcompressive stress regions, although enriched in the second alkali metalions, further comprise the first metal alkali metal ions. The secondsize may be greater than the first size and the third size may begreater than the second size.

In embodiments, the component includes an ion exchangeable glass orglass ceramic. Ion exchangeable glasses include, but are not limited to,soda lime glasses, aluminosilicate glasses, and aluminoborosilicateglasses. Ion exchangeable glass ceramics include, but are not limitedto, aluminosilicate glass ceramics and aluminoborosilicate glassceramics.

FIG. 5A shows a detailed view of the inset 1-1 of FIG. 3A for an exampleglass cover member 520 having an internal compressive stress regioncreated at least in part by an ion exchange process. The glass covermember 520 comprises an outer portion 538, portion 536 inward from outerportion 538, and inner portion 532 inward from portion 536. As shown inFIG. 5A, inner portion 532 may be centrally located. A first part ofouter portion 538 is adjacent front surface 522; a second part of outerportion 538 is adjacent back surface 524. The side surface of the covermember is not shown in this field of view. The alkali metal ions presentin the glass cover member are schematically illustrated, but the glassnetwork is not shown.

Prior to the ion exchange process, the cover member may be an ionexchangeable glass comprising first alkali metal ions 561. Asschematically shown in FIG. 5A, inner portion 532 of the cover member520 includes first alkali metal ions 561 and second alkali metal ions562. The first alkali metal ions 561 have a first size and the secondalkali metal ions 562 have a second size greater than the first size.The second alkali metal ions 562 may have been introduced by the ionexchange process. Inner portion 532 is enriched in the second alkalimetal ions 562 as compared to portion 536. The inner portion 532 mayalso be enriched in the second alkali metal ions 562 as compared toportion 538.

Portion 536 of the cover member 520 includes first alkali metal ions561. Portion 536 may be depleted of the second alkali metal ions 562 andenriched in the first alkali metal ions 561 as compared to inner portion532. The portion 536 may also be enriched in the first alkali metal ions561 as compared to portion 538. The first alkali metal ions may comprisefirst alkali metal ions present in the glass prior to the ion exchangeprocess and additional first alkali metal ions introduced during the ionexchange process.

Outer portion 538 of the cover member 520 comprises third alkali metalions 563 having a third size greater than the first size and is enrichedin the third alkali metal ions 563 as compared to portion 536. Outerportion 538 may also be enriched in the third alkali metal ions 563 ascompared to portion 532. The second alkali metal ions 562 and the thirdalkali metal ions 563 may have been introduced by the ion exchangeprocess. Outer portion 538 may further include first alkali metal ions561. The first alkali metal ions 561 may comprise first alkali metalions present in the glass prior to the ion exchange process andadditional first alkali metal ions introduced during the ion exchangeprocess.

As an example, the first alkali metal ions 561 (M₁ ⁺) are lithium ions,the second alkali metal ions 562 (M₂ ⁺) are sodium ions, and the thirdalkali metal ions 563 (M₃ ⁺) are potassium ions. In embodiments, theouter portion 538 of the cover is enriched in potassium ions and theinner portion 532 is enriched in sodium ions as compared to the portion536.

FIG. 5B shows an example of the variation of residual stress along thethickness of the glass cover member 520 of FIG. 5A. The glass covermember 520 includes internal compressive stress region 542. Internalcompressive stress region 542 may be located in inner portion 532 of theglass cover member 520 and created because inner portion 532 is enrichedin the second alkali metal ions as compared to portion 536.

The glass cover member 520 further includes external compressive stressregion 544. External compressive stress region 544 may be located inouter portion 538 of the glass cover member 520 and created becauseouter portion 538 is enriched in the third alkali metal ions 563 ascompared to portion 536. As shown in FIG. 5B, a level of the compressivestress is greater in external compressive stress region 544 than ininternal compressive stress region 542.

The glass cover member 520 further comprises internal tensile stressregion 554 between external compressive stress region 544 and internalcompressive stress region 542. The tensile stress in internal tensilestress region 554 at least partially balances the compressive stress inthe glass cover member 520. Internal tensile stress region 554 is atleast partially located in portion 536 of the glass cover member 520. Insome embodiments, the internal tensile stress region 554 may extendslightly into inner portion 532 and/or outer portion 538 of the glasscover member 520.

Therefore, the internal compressive stress region 542 of the glass covermember 520 of FIGS. 5A-5B may comprise first alkali metal ions 561 andsecond alkali metal ions 562 and may be enriched in the second alkalimetal ions 562 as compared to internal tensile stress region 554.Internal tensile stress region 554 may comprise first alkali metal ions561. Second alkali metal ions 562 and/or third alkali metal ions 563 maybe present in internal tensile stress region 554, but to a lesser amountas compared to the external compressive stress region 544 and theinternal compressive stress region 542. External compressive stressregion 544 may comprise first alkali metal ions 561 and third alkalimetal ions 563 and may be enriched in the third alkali metal ions 563 ascompared to internal tensile stress region 554.

FIG. 6 illustrates a flowchart of an example process 600 for making aninternal compressive stress region in a component using multiple ionexchange operations. Process 600 further creates an external compressivestress region and an internal tensile stress region. For example,process 600 may be used to form the glass cover member of FIGS. 5A-5B.

Process 600 includes multiple ion exchange operations. During each ionexchange operation, alkali metal ions in the component may be exchangedfor alkali metal ions in a bath. Alkali metal ions from the bath arethus introduced into the component. The bath may comprise a molten ionicsalt. The bath temperature may be from the melting point of the salt toapproximately 600° C.

The temperature of the bath may be below a strain point or a glasstransition point of a glass portion of the component, so that exchangingthe alkali metal ions in the component with larger alkali metal ionstends to cause an expansion of an ion-exchanged portion of thecomponent. However, expansion of the ion-exchanged portion of thecomponent may be constrained by other portions of the component whichare not ion exchanged. As a result, a compressive stress region, such asa biaxial residual compressive stress region, may be created in theion-exchanged portion. For example, the ion-exchanged portion may be inthe form of an ion-exchanged layer.

The process 600 may include operation 602 of exchanging first alkalimetal ions in an ion exchangeable portion of the component with secondalkali metal ions. The first alkali metal ions have a first size and thesecond alkali metal ions have a second size larger than the first size.The first alkali metal ions may be exchanged for the second alkali metalions by immersing the component in a bath comprising the second alkalimetal ions. The second alkali metal ions are thus introduced into thecomponent.

For example, operation 602 may be a first ion exchange operation whichforms a first ion exchange layer which extends throughout a thickness ofthe glass component. As another example, the first ion exchange layermay extend to a first exchange depth which is less than half a thicknessof the glass component. For example, the first alkali metal ions may belithium ions, the second alkali metal ions may be sodium ions, and thefirst ion exchange layer may comprise sodium ions which have beenintroduced into the glass via the first ion exchange operation. FIG. 7Bschematically illustrates an example distribution of the first andsecond alkali metal ions after operation 602.

The process 600 may further include operation 604 of exchanging secondalkali metal ions in the component with first alkali metal ions.Operation 604 may follow operation 602. Operation 604 may be a secondion exchange which forms a second ion exchange layer. The second ionexchange layer extends to a second exchange depth less than the firstexchange depth. The second ion exchange may comprise immersing thecomponent in a bath comprising the first alkali metal ions. First alkalimetal ions may thus be re-introduced into the component. For example,the second ion exchange layer may be depleted of sodium ions andenriched in lithium ions as compared to the first ion exchange layer.

In addition, process 600 may include operation 606 of exchanging secondalkali metal ions in the component with third alkali metal ions.Operation 606 may further include exchanging first alkali metal ions inthe component with the third alkali metal ions. Ion exchange operation606 may be a third ion exchange which forms a third ion exchange layer.The third ion exchange layer extends to a third exchange depth less thanthe second exchange depth. Operation 606 may comprise immersing thecomponent in a bath comprising the third alkali metal ions. Operation606 may follow operation 604 or may occur concurrently with operation604, in which case the bath may comprise the first alkali metal ions andthe third alkali metal ions. For example, the third alkali metal ionsmay be potassium ions and the third ion exchange layer may be enrichedin potassium ions as compared to the second ion exchange layer. FIG. 7Bschematically illustrates an example distribution of the first, second,and third alkali metal ions after operations 604 and 606.

FIGS. 7A, 7B, and 7C schematically illustrate three stages in an exampleprocess for creating an internal compressive stress region in a glasscover using multiple ion exchange operations. FIG. 7A shows a detailedview of a part of a glass cover member 720 prior to the first ionexchange. The glass cover member 720 comprises first alkali metal ions761 distributed across the thickness of the glass cover member 720. Thefield of view of FIGS. 7A-7C shows front surface 722 and back surface724, but not the side surface of the glass cover member.

FIG. 7B shows the glass cover member 720 of FIG. 7A following anexchange of at least some of the first alkali metal ions 761 with secondalkali metal ions 762 having a second size greater than the first size.For example, FIG. 7B may show the glass cover member after operation 602of process 600. As shown, the first ion exchange occurs throughout thethickness of the glass cover member 720. However, a greater amount ofexchange occurs near front surface 722 and back surface 724, so that theglass cover member 720 is depleted of the first alkali metal ions 761and enriched in the second alkali metal ions 762 near the front surface722 and the back surface 724. For example, the glass cover member 720may be substantially depleted of first alkali metal ions 761 in portion737 of the glass cover member 720. A remainder portion 733 of the glasscover member 720 comprises the first alkali metal ions 761 and thesecond alkali metal ions 762.

FIG. 7C shows the glass cover member 720 of FIG. 7B after a second and athird ion exchange which occur concurrently. For example, FIG. 7C mayshow the glass cover member after operations 604 and 606 of process 600.During the second ion exchange, at least some of the second alkali metalions 762 are exchanged for first alkali metal ions 761 to a secondexchange depth DE₂ less than half the thickness of the glass covermember 720. During the third ion exchange, at least some third alkalimetal ions 763 having a third size larger than the second size areexchanged for second alkali metal ions 762, first alkali metal ions 761,or a combination thereof to third exchange depth DE₃ which is less thanDE₂. For example, the glass cover member 720 may be immersed in a bathcomprising the first alkali metal ions 761 and the third alkali metalions 763 to achieve the second and third ion exchanges.

As a result, inner portion 732 of the glass cover member 720 comprisesthe first alkali metal ions 761 and the second alkali metal ions 762.Portion 736 comprises the first alkali metal ions 761 and is depleted ofthe second alkali metal ions 762 as compared to inner portion 732. Outerportion 738 of the glass cover member 720 comprises the third alkalimetal ions 763 and the first alkali metal ions 761 and is enriched inthe third alkali metal ions 763 as compared to portion 736. Thecomposition profile of FIG. 7C can produce an internal compressivestress region in portion 732, as previously discussed with respect toFIGS. 5A and 5B.

FIG. 8A shows a detailed view of the inset 2-2 of FIG. 4A for an exampleglass cover member 820 having internal compressive stress regionscreated at least in part by an ion exchange process. The glass covermember 820 comprises outer portion 838, portion 836 inward from outerportion 838, portion 834 inward from portion 836, and inner portion 832.A first part of outer portion 838 is adjacent front surface 822; asecond part of outer portion 838 is adjacent back surface 824. The sidesurface of the glass cover member 820 is not shown in this field ofview. Prior to the ion exchange process, the glass cover member 820 maycomprise an ion exchangeable glass comprising first alkali metal ions861.

As shown in FIG. 8A, an inner portion 832 of the glass cover member 820comprises first alkali metal ions 861 after the ion exchange process.The first alkali metal ions 861 may comprise first alkali metal ions 861present in the glass prior to the ion exchange process. The first alkalimetal ions 861 have a first size.

Portion 834 of the glass cover member 820 comprises first alkali metalions 861 and second alkali metal ions 862. The second alkali metal ions862 have a second size greater than the first size. The second alkalimetal ions 862 may have been introduced by the ion exchange process.Portion 834 is enriched in the second alkali metal ions 862 and depletedof the first alkali metal ions 861 as compared to portion 832. Portion834 may also be enriched in the second alkali metal ions 862 as comparedto portion 836.

Portion 836 of the glass cover member 820 comprises first alkali metalions 861. Portion 836 may be depleted of the second alkali metal ions862 and enriched in the first alkali metal ions 861 as compared toportion 834. Portion 836 may also be enriched in the first alkali metalions 861 as compared to portion 838. The first alkali metal ions 861 maycomprise first alkali metal ions 861 present in the glass prior to theion exchange process and additional first alkali metal ions 861introduced during the ion exchange process.

Outer portion 838 of the glass cover member 820 comprises first alkalimetal ions 861 and third alkali metal ions 863 having a third sizegreater than the first size. Outer portion 838 is enriched in the thirdalkali metal ions 863 as compared to portion 836. Outer portion 838 mayalso be enriched in the third alkali metal ions 863 as compared toportions 834 and 832.

As an example, the first alkali metal ions 861 (M₁ ⁺) are lithium ions,the second alkali metal ions 862 (M₂ ⁺) are sodium ions, and the thirdalkali metal ions 863 (M₃ ⁺) are potassium ions. In embodiments, theouter portion 838 of the cover is enriched in potassium ions as comparedto the portion 836 and the portion 834 is enriched in sodium ions ascompared to the portions 832 and 836.

FIG. 8B shows an example of the variation of residual stress along thethickness of the glass cover member 820 of FIG. 8A. The glass covermember 820 includes internal compressive stress region 842. Internalcompressive stress region 842 may be located in portion 834 of the glasscover member 820 and created because portion 834 is enriched in thesecond alkali metal ions 862 as compared to portion 836 and innerportion 832.

The glass cover member 820 further includes external compressive stressregion 844. External compressive stress region 844 may be located inouter portion 838 of the glass cover member 820 and created becauseouter portion 838 is enriched in the third alkali metal ions 863 ascompared to portion 836. As shown in FIG. 8B, a level of the compressivestress is greater in external compressive stress region 844 than ininternal compressive stress region 842.

The glass cover member 820 further comprises internal tensile stressregion 854 between external compressive stress region 844 and internalcompressive stress region 842. The tensile stress in internal tensilestress region 854 at least partially balances the residual compressivestress in the glass cover member 820. Internal tensile stress region 854is at least partially located in portion 836 of the glass cover member820. In some embodiments, internal tensile stress region 854 may extendslightly into inner portion 832 and/or outer portion 838 of the glasscover member. The glass cover member 820 further comprises internaltensile stress region 852 inward from internal compressive stress region842. The tensile stress in internal tensile stress region 852 at leastpartially balances compressive stress in the glass cover member 820 andis at least partially located in inner portion 832 of the glass covermember 820.

Therefore, the internal compressive stress region 842 of the glass covermember 820 of FIGS. 8A-8B may include second alkali metal ions and maybe enriched in the second alkali metal ions as compared to internaltensile stress regions 854 and 852. Internal tensile stress regions 854and 852 may include first alkali metal ions. Internal compressive stressregion 842 may further include first alkali metal ions, but may bedepleted in the first alkali metal ions as compared to internal tensilestress regions 854 and 852.

External compressive stress region 844 may comprise third alkali metalions and may be enriched in the third alkali metal ions as compared tointernal tensile stress region 854. External compressive stress region844 may further comprise first alkali metal ions, but may be depleted inthe first alkali metal ions as compared to internal tensile stressregion 854.

FIGS. 9A, 9B, and 9C schematically illustrate three stages in an exampleprocess for creating an internal compressive stress region in acomponent using multiple ion exchange operations. For example, theprocess may be used to produce the component of FIGS. 8A and 8B. FIG. 9Ashows the glass cover member 920 prior to ion exchange; the glass covermember 920 comprises first alkali metal ions 961 distributed across thethickness of the glass cover member 920. The field of view of FIGS.9A-9C shows front surface 922 and back surface 924 of the glass covermember 920, but not the side surface.

FIG. 9B shows the glass cover member 920 after a first ion exchange.During the first ion exchange at least some of the first alkali metalions 961 are exchanged with second alkali metal ions 962 having a secondsize greater than the first size to a first ion exchange depth DE₁ lessthan half the thickness of the glass cover member 920. As shown, theexchange does not occur throughout the thickness of the glass covermember 920 but occurs in portions 933. A greater amount of exchangeoccurs near front surface 922 and back surface 924, so that the glasscover member 920 is depleted of the first alkali metal ions 961 andenriched in the second alkali metal ions 962 near the front surface 922and the back surface 944. A remainder portion 931 of the glass covermember 920 is not substantially ion exchanged and comprises the firstalkali metal ions 961, but comprises few, if any, of the second alkalimetal ions 962.

FIG. 9C shows the glass cover member 920 after a second and a third ionexchange which occur concurrently. During the second ion exchange, atleast some of the second alkali metal ions 962 are exchanged for firstalkali metal ions 961 to a second exchange depth DE₂ less than the firstion exchange depth DE₁. During the third ion exchange, at least some ofthe third alkali metal ions 963 having a third size larger than thesecond size are exchanged for second alkali metal ions 962, first alkalimetal ions 961, or a combination thereof to a third exchange depth DE₃which is less than DE₂. For example, the glass cover member 920 may beimmersed in a bath comprising the first alkali metal ions 961 and thethird alkali metal ions 963 to achieve the desired ion exchange.

As a result, inner portion 932 of the glass cover member 920 comprisesthe first alkali metal ions 961. Portion 934 of the glass cover member920 comprises the first alkali metal ions 961 and the second alkalimetal ions 962. Portion 936 comprises the first alkali metal ions and isdepleted of the second alkali metal ions as compared to portion 934.Outer portion 938 of the glass cover member 920 comprises the thirdalkali metal ions 963 and the first alkali metal ions 961 and isenriched in the third alkali metal ions 963 as compared to portion 936.The composition profile of FIG. 9C can produce an internal compressivestress region within portion 934, as previously discussed with respectto FIGS. 8A and 8B.

In embodiments, crystallizing an internal portion of a glass componentto form a glass ceramic can create an internal compressive stress regionin the component. Selective crystallization of an internal portion of aglass component can create an internal glass ceramic portion havingdifferent properties than external portions of the cover member and aninternal compressive stress region in the internal glass ceramicportion. For example, if the crystals have a lower coefficient ofthermal expansion than the glass from which they are formed, theinternal glass ceramic portion of the component tends to contract lessthan the external glass portions when cooled from a crystallizationtemperature. As a result, compressive stresses can form in the internalglass ceramic portion of the component. The glass component may be ionexchangeable as well as crystallizable.

As an example, a component comprises an internal compressive stressregion located in the internal glass ceramic portion. The componentfurther comprises an external compressive stress region along anexternal surface of the component and an internal tensile stress regioninward from the external compressive stress region. The externalcompressive stress region can be formed by an ion exchange operation inthe external glass portion of the component.

The external portions of the component may each include a sufficientlylow volume of crystals to be considered a glass. The external glassportion of the component may comprise first alkali metal ions. Theexternal compressive stress region may include second alkali metal ionshaving a second size greater than the first size. The second alkalimetal ions may have been introduced by an ion exchange operation. Theinternal compressive stress region may include the first alkali metalions. For example, the first alkali metal ions may be lithium ions andthe second alkali ions may be potassium ions.

As another example, a strengthened glass component comprises an internalglass ceramic portion, a first external glass portion, and a secondexternal glass portion. The first external glass portion and the secondexternal glass portion may each comprise an aluminosilicate or analuminoborosilicate glass including first alkali metal ions having afirst size. For example, the first alkali metal ions may be lithiumions.

The strengthened glass component may comprise a first and a secondexternal compressive stress region, the first external compressivestress region along a first external surface and the second externalcompressive stress region along a second external surface. The firstexternal compressive stress region is located in the first externalglass portion and the second external compressive stress region islocated in the second external glass portion. The first and the secondexternal compressive stress regions can be formed by an ion exchangeoperation to introduce second alkali metal ions in the first and secondexternal glass portions of the component. For example, the second alkalimetal ions may be potassium ions.

The strengthened glass component may further comprise a first and asecond internal tensile stress region, the first internal tensile stressregion inward from the first external compressive stress region and thesecond internal tensile stress region inward from the second externalcompressive stress region. The first and second internal tensile stressregions may each include first alkali metal ions having a first size.

The strengthened glass component may further comprise an internalcompressive stress region inward from the first and the second internaltensile stress regions. The internal compressive stress region includesthe glass ceramic. The internal compressive stress region may alsoinclude the first alkali metal ions.

In embodiments, the glass component is capable of crystallization toform an internal glass ceramic portion. For example, the glass may be analuminosilicate glass capable of forming an aluminosilicate glassceramic or a boroaluminosilicate glass capable of forming aboroaluminosilicate glass ceramic. For example, the glass ceramic may bea lithium aluminosilicate (LAS). In embodiments, the internal glassceramic portion may include a residual glass phase and crystals of oneor more crystalline phases. The volume percentage of the crystals may below enough to prevent cracking of the residual glass phase duringcooling of the glass ceramic to room temperature (e.g., about 20° C.)but high enough to create a residual compressive stress. The crystalsmay be small enough so that the cover member remains transparent tovisible radiation.

FIG. 10A shows a detailed view of the inset 1-1 of FIG. 3A for anexample cover member having an internal compressive stress regioncreated at least in part by forming an internal glass ceramic portionwithin the cover member. The cover member 1020 comprises internal glassceramic portion 1032; portion 1032 comprises a glass ceramic. The glassceramic may include a residual glass phase and one or more crystallinephases. Crystals 1072 in FIG. 10A represent the crystalline phase; thecrystals 1072 are not necessarily shown to scale. In an embodiment, theglass ceramic includes first alkali metal ions 1061 having a first size.For convenience, first alkali metal ions 1061 having a first size areshown in the residual glass phase 1074. However, first alkali metal ions1061 may also be present in the crystals 1072.

As examples, glass ceramic portion 1032 may have a volume percentage ofcrystals 1072 greater than or equal to 30% and less than 100%, greaterthan or equal to 50% and less than 100%, or greater than or equal to 75%and less than 100%. The crystals 1072 may have an average size of lessthan about 50 nm to provide transparency to visible radiation.

In embodiments, the glass ceramic is an aluminosilicate glass ceramic oran aluminoborosilicate glass ceramic. The residual glass portion may bean aluminosilicate glass or an aluminoborosilicate glass. As an example,the glass from which the glass ceramic is formed may be a lithiumaluminosilicate glass and the glass ceramic may be a lithiumaluminosilicate glass ceramic. Lithium aluminosilicate glasses can formseveral types of crystals, including β quartz solid solution crystals, βspodumene solid solution crystals, and keatite solid solution crystals.The resulting crystals may have a coefficient of thermal expansion whichis close to zero or even less than zero.

The cover member 1020 of FIG. 10A also comprises an outer portion 1038and portion 1036. Outer portion 1038 and portion 1036 may cooperate toform an external glass portion of the cover member. Both outer portion1038 and portion 1036 may comprise a glass, such as an aluminosilicateor an aluminoborosilicate glass. The aluminosilicate or analuminoborosilicate glass may include first alkali metal ions 1061having a first size. Portion 1036 may include the first alkali metalions 1061. Outer portion 1038 may further comprise second alkali metalions 1062 having a second size. The second alkali metal ions 1062 may beintroduced into the outer portion 1038 through an ion exchange process.

FIG. 10B shows an example of the variation of residual stress withposition in the sample for the cover member 1020 of FIG. 10A. The covermember 1020 comprises external compressive stress region 1044 locatedalong surfaces 1022 and 1024 The cover member 1020 further comprises aninternal tensile stress region 1054 inward of external compressivestress region 1044. The cover member 1020 further comprises an internalcompressive stress region 1042 inward of internal tensile stress region1054.

External compressive stress region 1044 is in outer portion 1038 of thecover member 1020. The tensile stress in internal tensile stress region1054 balances the residual compressive stress in the glass cover member1020 and is at least partially located in portion 1036 of the covermember. In some embodiments, the internal tensile stress region 1054 mayextend slightly into inner portion 1032 and/or outer portion 1038 of thecover member 1020. As shown in FIG. 10B, a level of the compressivestress is greater in external compressive stress region 1044 than ininternal compressive stress region 1042. The internal compressive stressregion 1042 is located in inner glass ceramic portion 1032.

FIG. 11 illustrates a flowchart of an example process 1100 for making aninternal compressive stress region in a component using a combination ofselective crystallization of a glass ceramic and ion exchange. Process1100 further creates an external compressive stress region and aninternal tensile stress region. For example, process 1100 may be used toform the glass cover member of FIGS. 10A-10B.

The process 1100 may include operation 1102 of forming a glass ceramicin an internal portion of a glass component. Operation 1102 includes theoperation of forming crystals of the glass ceramic in the internalportion of the glass component. In embodiments, the operation of formingcrystals of the glass ceramic may include the operation of creatingcrystal nuclei followed by the operation of growing the crystal nucleito form crystals of a desired size. The operation of creating thecrystal nuclei may comprise heating the internal portion of the glasscomponent to a first temperature at which crystal nuclei form. Theoperation of growing the crystal nuclei may comprise heating theinternal portion to a second temperature. The second temperature may begreater than the first temperature.

The internal portion of the glass component may be heated at least inpart using a beam of radiation, such as a beam of light. For example, alaser may be used to heat the internal portion to a sufficienttemperature to nucleate and/or grow crystals in the glass. An adjacentportion of the glass component may be heated to a lesser extent. Forexample, nucleation and/or growth of crystals in the adjacent portion ofthe glass component may occur to a lesser extent. For example, thevolume percentage of crystals in the adjacent portion may be less thanin the adjacent portion of the glass. For example, a volume percentageof crystals in the internal portion may be at least 25%, 50% or 75%higher than in an external portion of the component. The beam ofradiation may be used in conduction with one or more additional heatsources (e.g., a furnace).

Process 1100 may further include operation 1104 of exchanging firstalkali metal ions in an outer portion of the component with secondalkali metal ions. The first alkali metal ions have a first size and thesecond alkali metal ions have a second size larger than the first size.The first alkali metal ions may be exchanged for the second alkali metalions by immersing the component in a bath comprising the second alkalimetal ions. For example, the exchange of ions may form an ion exchangelayer which extends to an exchange depth less than a depth of the glassceramic portion of the component.

FIGS. 12A, 12B, and 12C schematically illustrate three stages in anexample process for creating an internal compressive stress region in acomponent using a combination of selective crystallization of a glassceramic and ion exchange. FIGS. 12A and 12B illustrate exampleoperations of forming crystals of the glass ceramic using a beam ofradiation. Prior to exposing a cover member to the beam of radiation,the cover member comprises a glass including a first alkali metal ion1261 throughout a thickness of the glass component. The entirety ofcover member 1220 is not shown in FIGS. 12A-12C in order to provide amore detailed view.

FIG. 12A illustrates an example of forming crystals of the glass ceramicin an internal portion of the glass component. In FIG. 12A, beam 1282heats inner portion 1232 of cover member 1220. As a result, crystals1272 form in inner portion 1232, but not in portions 1235. As shown inFIG. 12A, beam 1282 may be a broad beam configured to deliver energy toa relatively large area. The beam 1282 may be provided by a laser, suchas a gas laser, a chemical laser, a solid state laser, a fiber laser, aphotonic crystal laser, or a semiconductor laser. The beam 1282 maydeliver energy to the component through side surface 1226, which joinsfront surface 1222 and back surface 1224.

FIG. 12B illustrates another example of forming crystals of the glassceramic in an internal portion of the glass component using a beam ofradiation. As in FIG. 12A, beam 1282 heats inner portion 1232 of covermember 1220. As a result, crystals 1272 form in inner portion 1232, butnot in portions 1235. As shown in FIG. 12B, the beam 1282 may be focusedto create focused beam 1284 which can deliver energy to a narrower beamspot. One or more lenses may be used to focus beam 1282. The focusedbeam 1284 may deliver energy to the component through a surface of thecomponent, such as front surface 1222. The focused beam 1284 may bemoved over the cover member 1220 to form crystals 1274 in inner portion1232.

FIG. 12C illustrates the cover member 1220 after the operation of ionexchanging first alkali metal ions in an outer portion of the componentwith second alkali metal ions. The first alkali metal ions have a firstsize and the second alkali metal ions have a second size larger than thefirst size. For example, the exchange of ions may form an ion exchangelayer which extends to an exchange depth DE₁ less than a depth of theglass ceramic portion of the component.

As a result, inner portion 1232 of the glass cover member 1220 comprisescrystals 1272 of the glass ceramic and first alkali metal ions 1261.Outer portion 1238 of the glass cover member 1220 comprises the firstalkali metal ions 1261 and the second alkali metal ions 1262. Portion1236 comprises the first alkali metal ions 1261 and is depleted of thesecond alkali metal ions 1262 as compared to outer portion 1238. Thecomposition and phase profile of FIG. 12C can produce an internalcompressive stress region within inner portion 1232, as previouslydiscussed with respect to FIGS. 10A and 10B.

FIG. 13A shows a detailed view of the inset 2-2 of FIG. 4A for anexample cover member 1320 having an internal compressive stress regioncreated at least in part by forming a glass ceramic region within thecover member 1320. The cover member 1320 comprises portion 1334including crystals 1372 of the glass ceramic. The cover member 1320 ofFIG. 13A also comprises an outer portion 1338, portion 1336 inward fromouter portion 1338, and inner portion 1332. Outer portion 1338, portion1336, and inner portion 1332 each may comprise a glass, such as analuminosilicate or an aluminoborosilicate glass. Portion 1336 maycomprise first alkali metal ions having a first size. The outer portion1338 may further comprise second alkali metal ions having a second sizeand may be enriched in the second alkali metal ions as compared toportion 1336. The second alkali metal ions may be introduced into theouter portion 1338 through an ion exchange process.

FIG. 13B shows an example of the variation of residual stress withposition in the sample for the glass cover member of FIG. 13A. Internalcompressive stress region 1342 may be located in portion 1334 andcreated by formation of the glass ceramic. External compressive stressregion 1344 may be located in outer portion 1338 and created as a resultof an ion exchange operation. As shown in FIG. 13B, a level of thecompressive stress is greater in external compressive stress region 1344than in internal compressive stress region 1342.

The cover member 1320 further comprises an internal tensile stressregion 1354 between the internal compressive stress region 1342 and theexternal compressive stress region 1344. The tensile stress in internaltensile stress region 1354 at least partially balances the residualcompressive stress in the cover member 1320. Internal tensile stressregion 1354 is at least partially located in portion 1336 of the covermember 1320. In some embodiments, the internal tensile stress region1354 may extend slightly into inner portion 1332 and/or outer portion1338 of the glass cover member 1320. The cover member 1320 furthercomprises internal tensile stress region 1352 inward from internalcompressive stress region 1342. The tensile stress in internal tensilestress region 1352 at least partially balances the residual compressivestress in the glass cover member. Internal tensile stress region 1352 isat least partially located in inner portion 1332 of the cover member1320.

In embodiments, at least one of the internal compressive stress regionsmay be created in a laminate component comprising layers havingdifferent compositions and/or properties. In further embodiments, aninternal compressive stress region may be created in an inner layer of aglass component having different thermal expansion and/or ion expansionproperties than outer layers of the glass component. As another example,the glass laminate component comprises a first outer layer formed from afirst glass material, an inner layer formed from a second glassmaterial, and a second outer layer formed from a third glass material.Alternately, each of these glass materials may be referred to as aglass. The second glass material may be the same as or different fromthe third glass material. Each of the inner layer, the first outerlayer, and the second outer layer may have a thickness.

The glass component may further comprise an external compressive stressregion, an internal tensile stress region inward from the externalcompressive stress region, and an internal compressive stress regioninward from the internal tensile stress region. As an example, the firstouter layer of the component includes the external compressive stressregion. The second outer layer of the component may also include theexternal compressive stress region. The external compressive stressregion may extend from a surface of the glass component to a first depthin the component. The internal compressive stress layer may be locatedin the inner layer. For example, the internal compressive stress layermay extend from the second depth to the third depth. The internaltensile stress layer may extend from the first depth to the seconddepth.

The first outer layer of the component may extend from a first surfaceto the second depth in the component, with an interface between thefirst outer layer of the component and the inner layer of the componentlocated at the second depth. The second outer layer of the component mayextend from a second surface to the third depth in the component, withan interface between the second outer layer of the component and theinner layer of the component located at the third depth.

In further embodiments, the glass component may comprise a firstexternal compressive stress region and a second external compressivestress region and an internal compressive stress region. For example,the first external compressive stress region extends from a firstsurface to a first depth in the component and the second externalcompressive stress region extends from a second surface to a fourthdepth in the component. The glass component may further comprise a firstinternal tensile stress region extending from the first depth to asecond depth in the component, an internal compressive stress regionextending from the second depth to a third depth in the component, and asecond internal tensile stress region extending from the fourth depth tothe third depth of the component. The first outer layer may include thefirst external compressive stress region and the first internal tensilestress region. The second outer layer may include the second externalcompressive stress region and the second internal tensile stress region.The inner layer may include the internal compressive stress region.

In an example, the first outer layer of the component extends from thefirst surface to the second depth in the component, with an interfacebetween the first outer layer of the component and the inner layer ofthe component located at the second depth. The second outer layer of thecomponent extends from the second surface to the third depth in thecomponent, with an interface between the second outer layer of thecomponent and the inner layer of the component located at the thirddepth.

FIG. 14A illustrates formation of an internal compressive stress regionin an example glass laminate cover member 1420. As shown in FIG. 14A,the glass laminate cover member 1420 comprises inner layer 1425 andouter layers 1427. The inner layer 1425 may join each of the outerlayers 1427 at interface 1426. Inner layer 1425 may be formed from afirst glass material and each of the outer layers 1427 may be formed ofa second glass material. Each outer layer 1427 may comprise an outerportion 1438 and a portion 1436 inward from the outer portion 1438.Although outer portion 1438 and portion 1436 are both formed from thesecond glass material, the composition of outer portion 1438 may differfrom that of the second glass material due to ion exchange.

FIG. 14B shows an example of the variation of residual stress withposition in the sample for the glass laminate cover member 1420 of FIG.14A. The glass laminate cover member 1420 has an internal compressivestress region 1442 located in inner layer 1425. The internal compressivestress region 1442 is created as a result of differences in one or moreproperties between the first glass material and the second glassmaterial. An external compressive stress region 1444 is located in outerportion 1438 along surfaces 1422 and 1424. The external compressivestress region 1444 may be created by an ion exchange. An internaltensile stress region 1454 is located between the internal compressivestress region 1442 and the external compressive stress region 1444. Asshown in FIG. 14B, a level of the compressive stress is greater in theexternal compressive stress region 1444 than in internal compressivestress region 1442.

In embodiments, the laminate may comprise outer layers each having ahigher coefficient of thermal expansion than that of an inner layer. Asan example, the first glass material has a first coefficient of thermalexpansion, the second glass material has a second coefficient of thermalexpansion, and the third glass material has a third coefficient ofthermal expansion. The first coefficient of thermal expansion may belower than the second coefficient of thermal expansion and lower thanthe third coefficient of thermal expansion. The second coefficient ofthermal expansion may be the same as or different from the thirdcoefficient of thermal expansion. For example, the outer layers may havea coefficient of thermal expansion greater than that of the inner layerby at least 10%, 25%, or 50%. In embodiments, the first glass materialmay be a borosilicate glass and the second and third glass materials maybe aluminosilicate glasses. The difference between the coefficient ofthermal expansion of the outer layers and the inner layer may create acompressive stress region in the inner layer upon cooling of thelaminate from a lamination temperature. The difference between thecoefficient of thermal expansion of the outer layers and the inner layermay be limited to prevent cracking at the interface between the outerlayers and the inner layer.

FIGS. 15A and 15B schematically illustrate two stages in an exampleprocess for creating an internal compressive stress region in a glasslaminate cover member 1520. In this example, the first glass material ofinner layer 1525 has a lower coefficient of thermal expansion than thesecond glass material of the outer layers 1527. FIG. 15A illustrates theglass laminate cover member 1520 after formation of the laminate. As anexample, the layers of the laminate may be directly bonded to each otherwithout an interstitial bonding agent. As another example, the glasslaminate may include an interstitial bonding agent between layers suchas a glass frit. As shown in FIG. 15A, the second glass materialcomprises a first alkali metal ion 1561 having a first size. After theinner layer 1525 is laminated between the outer layers 1527 at alamination temperature, the glass laminate cover member 1520 is cooledto a lower temperature, such as room temperature. Cooling of the glasslaminate cover member 1520 creates an internal compressive stress regionin inner layer 1525 (indicated by the arrows facing each other) and anexternal tensile stress region in the outer layer 1527 (indicated by thearrows facing away from each other).

FIG. 15B shows the glass laminate cover member 1520 of FIG. 15A after anion exchange operation. In the ion exchange operation, at least some ofthe first alkali metal ions 1561 in each of the outer layers 1527 areexchanged with second alkali metal ions 1562 having a second sizegreater than the first size. The ion exchange occurs to a depth lessthan a thickness of each of the outer layers 1527. Outer portion 1538 ofglass laminate cover member 1520 is enriched in the second alkali metalions 1562 as compared to portion 1536. As indicated by the arrows, theion exchange creates external compressive stress regions; each externalcompressive stress region is located in an outer portion 1538 of each ofthe outer layers 1527 adjacent a surface 1522, 1524 of the glasscomponent. The ion exchange also creates internal tensile stressregions, each of the internal tensile stress regions at least partiallylocated in one of the outer layers between one of the externalcompressive stress regions and the internal compressive stress region.

In additional embodiments, the laminate may comprise an inner layerhaving a greater tendency to expand in response to ion exchange than theouter layers. For example, the inner layer may have a larger networkdilation coefficient than the outer layers. As an example, the firstglass material may have a first network dilation coefficient, the secondglass material may have a second network dilation coefficient, and thethird glass material may have a third network dilation coefficient. Thefirst network dilation coefficient may be greater than the secondnetwork dilation coefficient and the third network dilation coefficient.The second network dilation coefficient may be the same as or differentfrom the third network dilation coefficient. The network dilationcoefficient, also known as the linear network dilation coefficient, maybe given by

${B = {\frac{1}{3}\frac{1}{V}\frac{\partial V}{\partial C}}},$where V is the molar volume and C is the local concentration of thesubstituted alkali metal ion. For example, the inner layer may have alinear network dilation coefficient greater than that of the outerlayers of at least 10%, 25%, or 50%. The greater tendency for expansionin response to ion exchange can create a compressive stress region inthe inner layer after ion exchange of the laminate.

FIGS. 16A, 16B, and 16C schematically illustrate three stages in anexample process for creating an internal compressive stress region in aglass laminate cover member 1620. In this example, the inner layer 1625has a greater tendency to expand in response to ion exchange than theouter layers 1627. FIG. 16A illustrates the glass laminate cover member1620 after formation of the laminate. As shown in FIG. 16A, both theinner layer and the outer layers comprise first alkali metal ions 1661.

FIG. 16B illustrates the glass laminate cover member 1620 after a firstion exchange operation in which at least some of the first alkali metalions are exchanged with second alkali metal ions 1662 having a secondsize greater than the first size to a depth greater than a thickness ofthe outer glass layer 1627. As indicated by the arrows, the ion exchangecreates an internal compressive stress region.

FIG. 16C illustrates the glass laminate cover member 1620 after a secondion exchange operation in which at least some of the second alkali metalions 1662 are exchanged with third alkali metal ions 1663 having a thirdsize greater than the second size. The second ion exchange occurs to adepth less than a thickness of the outer layer 1627. Outer portion 1638of glass laminate cover member 1620 is enriched in the third alkalimetal ions 1663 as compared to portion 1636. As indicated by the arrows,the ion exchange creates external compressive stress regions; eachexternal compressive stress region is located in an outer portion 1638of each of the outer glass layers 1627 adjacent a surface 1624, 1622 ofthe glass component. The ion exchange also creates internal tensilestress regions, each of the internal tensile stress regions at leastpartially located in one of the outer glass layers between one of theexternal compressive stress regions and the internal compressive stressregion.

FIG. 17 is a block diagram of example components of an exampleelectronic device. The schematic representation depicted in FIG. 17 maycorrespond to components of the devices depicted in FIG. 1A-16C asdescribed above. However, FIG. 17 may also more generally representother types of electronic devices with a strengthened glass component asdescribed herein.

In embodiments, an electronic device 1700 may include sensors 1720 toprovide information regarding configuration and/or orientation of theelectronic device in order to control the output of the display. Forexample, a portion of the display 1714 may be turned off, disabled, orput in a low energy state when all or part of the viewable area of thedisplay 1714 is blocked or substantially obscured. As another example,the display 1714 may be adapted to rotate the display of graphicaloutput based on changes in orientation of the device 1700 (e.g., 90degrees or 180 degrees) in response to the device 1700 being rotated. Asanother example, the display 1714 may be adapted to rotate the displayof graphical output in response to the device 1700 being folded orpartially folded, which may result in a change in the aspect ratio or apreferred viewing angle of the viewable area of the display 1714.

The electronic device 1700 also includes a processor 1704 operablyconnected with a computer-readable memory 1702. The processor 1704 maybe operatively connected to the memory 1702 component via an electronicbus or bridge. The processor 1704 may be implemented as one or morecomputer processors or microcontrollers configured to perform operationsin response to computer-readable instructions. The processor 1704 mayinclude a central processing unit (CPU) of the device 1700. Additionallyand/or alternatively, the processor 1704 may include other electroniccircuitry within the device 1700 including application specificintegrated chips (ASIC) and other microcontroller devices. The processor1704 may be configured to perform functionality described in theexamples above. In addition, the processor or other electronic circuitrywithin the device may be provided on or coupled to a flexible circuitboard in order to accommodate folding or bending of the electronicdevice. A flexible circuit board may be a laminate including a flexiblebase material and a flexible conductor. Example base materials forflexible circuit boards include, but are not limited to, polymermaterials such as vinyl (e.g., polypropylene), polyester (e.g.,polyethylene terephthalate (PET), biaxially-oriented PET, andpolyethylene napthalate (PEN)), polyimide, polyetherimide,polyaryletherketone (e.g., polyether ether ketone (PEEK)), fluoropolymerand copolymers thereof. A metal foil may be used to provide theconductive element of the flexible circuit board.

The memory 1702 may include a variety of types of non-transitorycomputer-readable storage media, including, for example, read accessmemory (RAM), read-only memory (ROM), erasable programmable memory(e.g., EPROM and EEPROM), or flash memory. The memory 1702 is configuredto store computer-readable instructions, sensor values, and otherpersistent software elements.

The electronic device 1700 may include control circuitry 1706. Thecontrol circuitry 1706 may be implemented in a single control unit andnot necessarily as distinct electrical circuit elements. As used herein,“control unit” will be used synonymously with “control circuitry.” Thecontrol circuitry 1706 may receive signals from the processor 1704 orfrom other elements of the electronic device 1700.

As shown in FIG. 17, the electronic device 1700 includes a battery 1708that is configured to provide electrical power to the components of theelectronic device 1700. The battery 1708 may include one or more powerstorage cells that are linked together to provide an internal supply ofelectrical power. The battery 1708 may be operatively coupled to powermanagement circuitry that is configured to provide appropriate voltageand power levels for individual components or groups of componentswithin the electronic device 1700. The battery 1708, via powermanagement circuitry, may be configured to receive power from anexternal source, such as an alternating current power outlet. Thebattery 1708 may store received power so that the electronic device 1700may operate without connection to an external power source for anextended period of time, which may range from several hours to severaldays. The battery 1708 may be flexible to accommodate bending or flexingof the electronic device. For example, the battery 1708 may be mountedto a flexible housing or may be mounted to a flexible printed circuit.In some cases, the battery 1708 is formed from flexible anodes andflexible cathode layers and the battery cell is itself flexible. In somecases, individual battery cells are not flexible, but are attached to aflexible substrate or carrier that allows an array of battery cells tobend or fold around a foldable region of the device.

In some embodiments, the electronic device 1700 includes one or moreinput devices 1710. The input device 1710 is a device that is configuredto receive input from a user or the environment. The input device 1710may include, for example, a push button, a touch-activated button,capacitive touch sensor, a touch screen (e.g., a touch-sensitive displayor a force-sensitive display), capacitive touch button, dial, crown, orthe like. In some embodiments, the input device 1710 may provide adedicated or primary function, including, for example, a power button,volume buttons, home buttons, scroll wheels, and camera buttons.

The device 1700 may also include one or more sensors 1720, such as aforce sensor, a capacitive sensor, an accelerometer, a barometer, agyroscope, a proximity sensor, a light sensor, or the like. The sensors1720 may be operably coupled to processing circuitry. In someembodiments, the sensors 1720 may detect deformation and/or changes inconfiguration of the electronic device and be operably coupled toprocessing circuitry which controls the display based on the sensorsignals. In some implementations, output from the sensors 1720 is usedto reconfigure the display output to correspond to an orientation orfolded/unfolded configuration or state of the device. Example sensors1720 for this purpose include accelerometers, gyroscopes, magnetometers,and other similar types of position/orientation sensing devices. Inaddition, the sensors 1720 may include a microphone, acoustic sensor,light sensor, optical facial recognition sensor, or other types ofsensing device.

In some embodiments, the electronic device 1700 includes one or moreoutput devices 1712 configured to provide output to a user. The outputdevice 1712 may include display 1714 that renders visual informationgenerated by the processor 1704. The output device 1712 may also includeone or more speakers to provide audio output. The output device 1712 mayalso include one or more haptic devices that are configured to produce ahaptic or tactile output along an exterior surface of the device 1700.

The display 1714 may include a liquid-crystal display (LCD),light-emitting diode, organic light-emitting diode (OLED) display, anactive layer organic light emitting diode (AMOLED) display, organicelectroluminescent (EL) display, electrophoretic ink display, or thelike. If the display 1714 is a liquid-crystal display or anelectrophoretic ink display, the display 1714 may also include abacklight component that can be controlled to provide variable levels ofdisplay brightness. If the display 1714 is an organic light-emittingdiode or organic electroluminescent type display, the brightness of thedisplay 1714 may be controlled by modifying the electrical signals thatare provided to display elements. In addition, information regardingconfiguration and/or orientation of the electronic device may be used tocontrol the output of the display as described with respect to inputdevices 1710. In some cases, the display is integrated with a touchand/or force sensor in order to detect touches and/or forces appliedalong an exterior surface of the device 1700.

The electronic device 1700 may also include a communication port 1716that is configured to transmit and/or receive signals or electricalcommunication from an external or separate device. The communicationport 1716 may be configured to couple to an external device via a cable,adaptor, or other type of electrical connector. In some embodiments, thecommunication port 1716 may be used to couple the electronic device to ahost computer.

The electronic device 1700 may also include at least one accessory 1718,such as a camera, a flash for the camera, or other such device. Thecamera may be connected to other parts of the electronic device 1700such as the control circuitry 1706.

The following discussion applies to the electronic devices describedherein to the extent that these devices may be used to obtain personallyidentifiable information data. It is well understood that the use ofpersonally identifiable information should follow privacy policies andpractices that are generally recognized as meeting or exceeding industryor governmental requirements for maintaining the privacy of users. Inparticular, personally identifiable information data should be managedand handled so as to minimize risks of unintentional or unauthorizedaccess or use, and the nature of authorized use should be clearlyindicated to users.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the describedembodiments. However, it will be apparent to one skilled in the art thatthe specific details are not required in order to practice the describedembodiments. Thus, the foregoing descriptions of the specificembodiments described herein are presented for purposes of illustrationand description. They are not intended to be exhaustive or to limit theembodiments to the precise forms disclosed. It will be apparent to oneof ordinary skill in the art that many modifications and variations arepossible in view of the above teachings.

What is claimed is:
 1. A strengthened glass component for an electronicdevice, comprising: first alkali metal ions having a first size, secondalkali metal ions having a second size greater than the first size, andthird alkali metal ions having a third size greater than the secondsize; a first external surface defining at least a portion of anexterior of the electronic device; a first external compressive stressregion along the first external surface; a first internal tensile stressregion inward from the first external compressive stress region; a firstinternal compressive stress region inward from the first internaltensile stress region; a second external surface opposite to the firstexternal surface; a second external compressive stress region along thesecond external surface; a second internal tensile stress region inwardfrom the second external compressive stress region; a second internalcompressive stress region inward from the second internal tensile stressregion; and a third internal tensile stress region between the firstinternal compressive stress region and the second internal compressivestress region, wherein: the first, the second, and the third internaltensile stress regions each includes at least a respective portion ofthe first alkali metal ions; the first internal compressive stressregion and the second internal compressive stress region are enriched inthe second alkali metal ions as compared to the first, the second, andthe third internal tensile stress regions; and the first externalcompressive stress region and the second external compressive stressregion are enriched in the third alkali metal ions as compared to thefirst and the second internal tensile stress regions.
 2. Thestrengthened glass component of claim 1, wherein the strengthened glasscomponent is formed from a single piece of glass.
 3. The strengthenedglass component of claim 2, wherein: the strengthened glass componentcomprises an aluminosilicate or an aluminoborosilicate glass.
 4. Thestrengthened glass component of claim 1, wherein the first alkali metalions are lithium ions, the second alkali metal ions are sodium ions, andthe third alkali metal ions are potassium ions.
 5. The strengthenedglass component of claim 1, wherein the strengthened glass component ision-exchanged in each of the first and the second external compressivestress regions, the first and the second internal tensile stressregions, and the first and the second internal compressive stressregions.
 6. The strengthened glass component of claim 1, wherein athickness of the strengthened glass component is from 0.1 mm to 2 mm. 7.A strengthened component comprising: a first glass layer defining afirst surface of the strengthened component and including: anion-exchanged first portion along the first surface; a first externalcompressive stress region located within the ion-exchanged firstportion; a second portion inward of the ion-exchanged first portion andhaving a first coefficient of thermal expansion; and a first internaltensile stress region located at least partially within the secondportion; a second glass layer defining a second surface of thestrengthened component and including: an ion-exchanged third portionalong the second surface; a second external compressive stress regionlocated within the ion-exchanged third portion; a fourth portion inwardof the ion-exchanged third portion and having a second coefficient ofthermal expansion; and a second internal tensile stress region locatedat least partially within the fourth portion; and an inner layercomprising: a glass ceramic having a third coefficient of thermalexpansion less than the first and the second coefficients of thermalexpansion; and an internal compressive stress region located within theinner layer.
 8. The strengthened component of claim 7, wherein: each ofthe first glass layer and the second glass layer comprises analuminosilicate glass; and the inner layer comprises an aluminosilicateglass ceramic.
 9. The strengthened component of claim 8, wherein: eachof the second portion and the fourth portion comprises first alkalimetal ions having a first size; each of the ion-exchanged first portionand the ion-exchanged third portion comprises second alkali metal ionshaving a second size greater than the first size; and the first alkalimetal ions are lithium ions and the second alkali metal ions arepotassium ions.
 10. The strengthened component of claim 7, wherein thestrengthened component is formed from a single piece of glass.
 11. Thestrengthened component of claim 7, wherein the inner layer comprises avolume percentage of crystals from 30% to less than 100%.
 12. Thestrengthened component of claim 11, wherein the strengthened componentis transparent to visible light.
 13. The strengthened component of claim11, wherein the strengthened component is translucent.
 14. A method ofstrengthening a glass component for an electronic device, the methodcomprising: a first operation comprising exchanging a portion of firstalkali metal ions in the glass component with second alkali metal ionshaving a second size larger than a first size of the first alkali metalions, thereby forming a first ion-exchanged layer along a first surfaceand a second surface of the glass component; a second operationcomprising exchanging a portion of the second alkali metal ions in thefirst ion-exchanged layer with the first alkali metal ions, therebyforming a second ion-exchanged layer along the first and the secondsurfaces, the second ion-exchanged layer having a depth less than adepth of the first ion-exchanged layer; and a third operation comprisingexchanging a portion of the first alkali metal ions in the secondion-exchanged layer with third alkali metal ions, the third alkali metalions having a third size greater than the second size, thereby forming athird ion-exchanged layer along the first and the second surfaces, thethird ion-exchanged layer having a depth less than the depth of thesecond ion-exchanged layer, a resulting strengthened glass componentcomprising: a first external compressive stress region along the firstsurface and a second external compressive stress region along the secondsurface; a first internal compressive stress region and a secondinternal compressive stress region; a first internal tensile stressregion between the first external compressive stress region and thefirst internal compressive stress region; a second internal tensilestress region between the first internal compressive stress region andthe second internal compressive stress region; and a third internaltensile stress region between the second external compressive stressregion and the second internal compressive stress region.
 15. The methodof claim 14, wherein: each of the first internal compressive stressregion and the second internal compressive stress region is configuredto deflect a crack propagating through the first internal tensile stressregion or the second internal tensile stress region.
 16. The method ofclaim 14, wherein: the glass component comprises an aluminosilicate oran aluminoborosilicate glass including the first alkali metal ions; thefirst internal compressive stress region and the second internalcompressive stress region are enriched in the second alkali metal ionsas compared to the first, the second, and the third internal tensilestress regions; the first external compressive stress region and thesecond external compressive stress region are enriched in the thirdalkali metal ions as compared to the first and the second internaltensile stress regions; and each of the first internal tensile stressregion and the second internal tensile stress region includes arespective portion of the first alkali metal ions exchanged for theportion of the second alkali metal ions during the second operation. 17.The method of claim 14, wherein the second operation and the thirdoperation occur concurrently.
 18. The method of claim 14, wherein: thethird internal tensile stress region includes a midpoint of a thicknessof the glass component.
 19. The method of claim 14, wherein a maximumlevel of compressive stress in the first and the second externalcompressive stress regions is from 3 to 10 times a maximum level ofcompressive stress in the first and the second internal compressivestress regions.
 20. The method of claim 14, wherein the first alkalimetal ions are lithium ions, the second alkali metal ions are sodiumions, and the third alkali metal ions are potassium ions.